This invention relates to a magnetic recording/reproduction apparatus such as a floppy disk unit for use in an external storage of a computer or the like and, more particularly, to a motor for rotating a disk-like magnetic recording medium such as a floppy disk.
A conventional motor of this kind is known which has a construction such as that shown in FIG. 4. As shown in FIG. 4, a bearing housing 52 is provided integrally with a base 51, and outer races 54 of a pair of ball bearings 53 are fixed in the bearing housing 52 in a two-stepped manner. A rotating shaft 56 is fixed to inner races 55 by press fitting or bonding and is rotatably supported by the ball bearings 53. A stator 57 is attached to an outer peripheral portion of the bearing housing 52 by screws 58, and coil windings 59 are provided on the stator 57. A rotor 61 is fixed to a top end portion of the rotating shaft 56 through a bush 60. A magnet 62 having a magnetic field extending across the stator 57 is attached to the inner surface of an outer circumferential portion of the rotor 61.
The rotating members including the magnet 62, the rotor 61 and the rotating shaft 56 are rotated by causing a current to flow through the coil windings 59. By this rotation, the floppy disk (not shown) is rotated for recording or reproduction of information on or from the floppy disk.
Another conventional motor is known which has a construction wherein an oilless metal is used instead of one of the ball bearings to rotatably support the rotating shaft 56.
In the above-described constructions of the conventional motors, however, there is a gap between the rotating shaft 56 and the inner diametral surfaces of the inner races 55 of the ball bearings 53, and there is also a play in the radial direction in the ball bearings 53. For this reason, if the span between the bearings for supporting the rotating shaft 56 is reduced, the extent of whirling of the rotating shaft 56 is increased and the accuracy of the attitude of the rotating shaft 56 is reduced, resulting in failure to achieve the desired functions of the floppy disk unit. To maintain the desired accuracy with which the rotating shaft 56 rotates, it is necessary to set the bearing span to a substantially large distance. Accordingly, it is difficult to reduce the size of the floppy disk unit by reducing the overall thickness. There is also the problem of a comparatively short life of the ball bearings 53.